1. Field of the Invention
The present invention relates to fuel cell system provided with fuel cell stacks, in which a plurality of unit cells comprising a membrane electrode assembly having a pair of electrodes on both sides of an electrolyte are stacked horizontally so as to be interposed by separators.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell comprises a unit cell or cells, each having a membrane electrode assembly being interposed by the separators. Further, said membrane electrode assembly is comprised of an anode-side electrode and a cathode-side electrode to be provided on both sides of an electrolyte (electrolyte membrane) so as to be opposed each other, where said electrolyte is composed of a polymer ion-exchange membrane (positive ion-exchange membrane). This type of unit cell comprises membrane electrode assemblies and separators in general, a predetermined numbers of said assemblies and separators are alternately stacked on one another to constitute a fuel cell stack.
In the unit cell, a fuel gas, for example, mainly a gas containing hydrogen (referred below to as hydrogen containing gas), supplied to the anode-side electrode is ionized on an electrode catalyst and moved toward the cathode-side electrode through the electrolyte. Electrons generated in the meantime are taken into an external circuit to be made use of as a DC electric energy. In addition, since an oxidizer gas, for example, a gas mainly containing oxygen, or an air, (referred below to as oxygen containing gas) is supplied to the cathode-side electrode, hydrogen ions, electrons, and oxygen react on the cathode-side electrode to generate water.
By the way, in the case where a fuel cell stack is mounted in a vehicle for use, for example, many unit cells are required for being stacked in order to get a desired high output energy. In this occasion, it causes a problem such that unit cells are considerably extended in a stacking direction, whereby a fuel gas ends up being supplied insufficiently to the respective unit cells.
FIG. 7 illustrates a fuel cell as disclosed in JP-A-6-275307, paragraph 0012 and reference FIG. 1 (hereafter Patent Document 1) that comprises two stacks 1a, 1b which are directly arranged on a lower common clamp plate 2 for commonly connecting both the stacks. The stack 1a is set with the positive electrode to be disposed on a lower side while the stack 1b is set with the positive electrode to be disposed on an upper side, whereby serial connection of the stacks 1a and 1b can be made electrically by the lower common clamp plate 2. Moreover, an upper clamp plate 3a on the stack 1a is connected to a negative electrode terminal 4 and an upper clamp plate 3b on the stack 1b is connected to a positive electrode terminal 5, whereby the negative electrode terminal 4 and the positive electrode terminal 5 can be connected to each other.
The stacks 1a, 1b, respectively, comprise a plurality of unit cells 6a, 6b, which are stacked in a direction as indicated by an arrow X, and the manifolds 7a, 7b for supplying and discharging the reaction-gas, which are mounted on the respective sides of the stacks 1a, 1b. The manifolds 7a, 7b are provided with joints 8a, 8b, and each of the joints is connected to an external piping (not shown).
With the Patent Document 1, however, such manifolds 7a, 7b must be further provided in accordance with the specific purposes such as supplying and discharging a fuel gas, an oxidizer gas, and a coolant from the respective stacks 1a, 1b. Therefore, the piping system becomes complicated and large in size, and the whole size of the fuel cell stacks becomes also considerably large one. Thereby, space factor is decreased which pointed out a problem of the fuel cell disclosed in the Patent Document being not useful or efficient for the vehicle-mounting application.